Hemiancistrus subviridis

Hemiancistrus: from the Greek hemi, meaning 'half', and the genus name Ancistrus, for species that share some of the features of Ancistrus but not all of them.

subviridis: Latin for 'greenish', after the olive base colour of live fish (Werneke et al., 2005).

Upper Orinoco and Casiquiare drainages in Amazonas state, Venezuela. It's known from the Orinoco upstream of the Atures rapids as far as the río Iguapo, from the río Ventuari, and from the río Casiquiare upstream of the río Siapa (Werneke et al., 2005). The Catalog of Fishes also lists it from Colombia, where the Orinoco forms the border.

Type locality is 'río Orinoco 117 km W of La Esmeralda, 03.28998°N, 066.60004°W, Amazonas, Venezuela'.

Found most often in the cracks and gaps between granite rocks in flowing water (Werneke et al., 2005). At one site on the upper Orinoco, 2 m deep and sampled in early spring, the water was 32.4 °C and pH 7.04, with a conductivity below 50 µS/cm (Collins, PFK).

Baryancistrus demantoides and Hemiancistrus guahiborum live alongside it (Werneke et al., 2005).

Needs a tank of several hundred litres, especially for a breeding group (Collins, PFK).

Build the tank around rockwork, with rounded boulders, upright slabs of stone and plenty of cracks and caves. Provide more hiding places than there are fish, and silicone the rocks together so they can't collapse. A thin layer of sand and gravel is enough. Rooted plants rarely do well, but Java fern and Anubias can be grown on bogwood.

Use powerful external filters and circulation pumps aimed across the rockwork, as it does best in warm, well-oxygenated water with plenty of movement. Collins suggests a turnover of 10 to 20 times the tank volume per hour. Make large, frequent water changes and keep nitrate below 20 mg/l (Collins, PFK). It also adapts to calmer water in a community tank (PlanetCatfish).

Newly imported fish are often thin. Buy fish that are alert and feeding and have rounded bellies, and avoid any that shimmy or swim on the spot (Collins, PFK).

The gut contents of wild fish were mostly fine mineral and organic sediment, with fragments of moss, filamentous algae, wood, mayfly and midge larvae and insect remains (Werneke et al., 2005). It feeds by scraping algae, detritus and small invertebrates off the rocks (Collins, PFK).

In the aquarium it's an omnivore and easy to feed. Offer sinking algae wafers and good-quality dried foods with frozen bloodworm and Mysis, and always leave some blanched courgette or sweet potato in the tank (Collins, PFK; PlanetCatfish).

It's territorial, more so as it matures, and can be aggressive towards its own kind and other bottom-dwelling fish of a similar size (Collins, PFK). It's a little less quarrelsome with its own kind than B. demantoides (Schäfer, 2025). If you keep more than one, give each fish its own cave (Collins, PFK).

Choose tankmates that live higher in the water and cope with warm, fast-flowing water, such as pencilfishes, rummynose tetras, silver dollars or Semaprochilodus (Collins, PFK; PlanetCatfish).

Only mature fish in good condition can be sexed. Males grow larger than females and have a broader, heavier head, with thicker odontodes on the cheeks and pectoral-fin spines and some on the back behind the dorsal fin too (Collins, PFK).

Has been bred in the aquarium. It spawns in caves, so offer several of different sizes, such as clay caves, pipes or gaps in stacked rock. Fish start to breed at about half their full size (Collins, PFK).

The female lays 30 to 40 large yellowish eggs in the male's cave, and he guards the eggs and fry on his own (Collins, PFK; PlanetCatfish). The eggs hatch in three to five days, and the fry use up their yolk sacs and start feeding at 10 to 11 days (PlanetCatfish).

The fry are large enough to take soaked flake and crushed tablet food straight away. Feed them often and take out any leftover food, because they're sensitive to bacteria in the substrate (Collins, PFK).

It hybridises with B. demantoides in aquaria (Schäfer, 2025). If you want to breed it, buy all your fish from one source so different forms aren't mixed (Collins, PFK).

First imported in 1995 and sold as L200, the green phantom plec, for ten years before it was described (Collins, PFK).

L200 is also used for Baryancistrus demantoides, sometimes sold as 'L200 high-fin' or 'L200a'. Both species were described in the same paper and live in the same rivers. To tell them apart, look at the fins on the back. H. subviridis has a clear gap between the end of the dorsal fin and the adipose fin, and in B. demantoides a membrane joins them. H. subviridis also has fewer teeth, with 9 to 29 on each half of the lower jaw compared with 34 to 51 (Werneke et al., 2005). Dorsal-fin height and spotting vary in both species, so neither is reliable on its own (Schäfer, 2025).

It looks very like L128, the blue phantom plec, collected further north around Puerto Ayacucho. Along the river these fish run from bluish green in the north to yellowish green further south, and intermediate fish have been reported (Collins, PFK; PlanetCatfish; ScotCat). L128 may be a colour form of H. subviridis, but this hasn't been confirmed.

The genus Hemiancistrus contains several groups of species that aren't closely related (Werneke et al., 2005), so this fish may be moved to another genus in future.